|  | 6.1 | Access Control Lists (ACLs)
| 6.1.4 | How ACLs work
An ACL is a group of statements that define how packets: Enter inbound interfaces Relay through the router Exit outbound interfaces of the router The beginning of the communication process is the same, whether ACLs are used or not. As a packet enters an interface, the router checks to see whether the packet is routable or bridgeable. Now, the router checks whether the inbound interface has an ACL. If one exists, the packet is now tested against the conditions in the list. If the packet is allowed it will then be checked against routing table entries to determine the destination interface. Next, the router checks whether the destination interface has an ACL. If it does not, the packet can be sent to the destination interface directly; for example, if it will use E0, which has no ACLs, the packet uses E0 directly. ACL statements operate in sequential, logical order. If a condition match is true, the packet is permitted or denied and the rest of the ACL statements are not checked. If all the ACL statements are unmatched, an implicit "deny any" statement is imposed. This means that even though you will not see the "deny any" as the last line of an ACL, it is there.
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